However, some constants are defined with different physical dimensions in cgs
and cannot be directly converted. Because of this ambiguity, such constants
cannot be used in expressions without specifying a system:

>>> 100*const.eTraceback (most recent call last):...TypeError: Constant u'e' does not have physically compatible unitsacross all systems of units and cannot be combined with othervalues without specifying a system (eg. e.emu)>>> 100*const.e.esu<Quantity 4.8032045057134676e-08 Fr>

The astronomical and physical constants are combined into modules with
names like astropyconst13 and astropyconst20. To temporarily set
constants to an older version (e.g., for regression testing), a context
manager is available, as follows: